fix(select): losing focus position when tabbing away after clicking inside multi select

Fixes the user's focus position being lost when they click to toggle an option inside a multi-select and then tab away.

Fixes #10900.

Author: crisbeto

src/lib/select/select.spec.ts

@@ -912,6 +912,25 @@ describe('MatSelect', () => {
         expect(fixture.componentInstance.select.panelOpen).toBe(false);
       }));
 
+      it('should restore focus to the host before tabbing away', fakeAsync(() => {
+        const select = fixture.nativeElement.querySelector('.mat-select');
+
+        trigger.click();
+        fixture.detectChanges();
+        flush();
+
+        expect(fixture.componentInstance.select.panelOpen).toBe(true);
+
+        // Use a spy since focus can be flaky in unit tests.
+        spyOn(select, 'focus').and.callThrough();
+
+        dispatchKeyboardEvent(trigger, 'keydown', TAB);
+        fixture.detectChanges();
+        flush();
+
+        expect(select.focus).toHaveBeenCalled();
+      }));
+
       it('should close when tabbing out from inside the panel', fakeAsync(() => {
         trigger.click();
         fixture.detectChanges();

src/lib/select/select.ts

@@ -826,7 +826,13 @@ export class MatSelect extends _MatSelectMixinBase implements AfterContentInit,
       .withVerticalOrientation()
       .withHorizontalOrientation(this._isRtl() ? 'rtl' : 'ltr');
 
-    this._keyManager.tabOut.pipe(takeUntil(this._destroy)).subscribe(() => this.close());
+    this._keyManager.tabOut.pipe(takeUntil(this._destroy)).subscribe(() => {
+      // Restore focus to the trigger before closing. Ensures that the focus
+      // position won't be lost if the user got focus into the overlay.
+      this.focus();
+      this.close();
+    });
+
     this._keyManager.change.pipe(takeUntil(this._destroy)).subscribe(() => {
       if (this._panelOpen && this.panel) {
         this._scrollActiveOptionIntoView();